Planar Semiconductor Microcavities Research Articles

Photonic devices based on wide gap semiconductors for room temperature polariton emission

Planar semiconductor microcavities have found increasing attention since they allow to enhance and control the interaction between light and excitons. When the coupling between photon and exciton is strong enough, polaritons are formed which are observed in a pronounced Rabi-splitting in the cavity spectra. The strong exciton-light coupling regime, necessesary for polariton-based applications depends on the oscillator strength and the exciton binding energy. The wide-gap II–VI (CdTe,ZnSe and CdSe) as well as the group III-nitrides (GaN,InN and AlN) semiconductors excellently fulfil these conditions. We observed a large Rabi-splitting (about 44 meV) with ZnSe-based semiconductor microcavities containing four strained (Zn,Cd)Se quantum wells and ZnS/YF3 distributed Bragg-reflectors. Measurements of the reflectivity and of the photoluminescence revealed clear evidence of the strong coupling regime. We also report on first experiments to optimise the structural and optical properties of (Al,Ga)N/GaN quantum wells. The results obtained so far show that these structures may be used for the investigation of polariton Rabi-splitting at room temperature. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Tuning of exciton-photon coupling in a planarsemiconductor microcavity by applying hydrostatic pressure

By means of hydrostatic pressure tuning, we have observed thestrong-coupling exciton-polariton mode in a planar microcavity with an InGaAs/GaAs quantum well embedded in it, over a pressure rangefrom 0.37 to 0.41 GPa. The experimental data canbe fitted very well to a corresponding theoretical formula with a uniquevalue of the vacuum Rabi splitting equal to 6.0 meV. A comparisonbetween pressure tuning and other tuning methods is madeas regards to what extent the intrinsic featuresof the exciton and cavity will be influenced during the tuningprocedure.

Room temperature enhancement and inhibition of spontaneous emission in semiconductor microcavities

We have fabricated planar semiconductor microcavities with metallic mirrors in which we have observed both enhancement and inhibition of spontaneous emission, at room temperature. Our results are quantitatively accounted for by modeling the band-to-band emission as arising from point dipoles. Observation of these cavity quantum electrodynamics effects in room temperature semiconductor structures opens the way to optoelectronic devices with controlled spontaneous emission.

SEMICLASSICAL THEORY OF EXCITONIC POLARITONS IN A PLANAR SEMICONDUCTOR MICROCAVITY

We present a comprehensive theoretical description of quantum well exciton–polaritons imbedded in a planar semiconductor microcavity. The exact nonlacal dielectric response of the quantum well exciton is treated in detail. The 4-spinor structure of the hole subband in the quantum well is considered, including the pronounced band mixing effect. The scheme is self-contained and can be used to treat different semiclassical aspects of the microcavity properties. As an example, we analyze the "selection" rules for the exciton–cavity mode coupling for different excitons.

Propagation of Nonclassical Light through a Semiconductor Microcavity

We extend recently developed schemes for field quantization in absorbing dielectric media with local susceptibilities to dielectric systems described by a nonlocal susceptibility, in order to quantize the electromagnetic field in quantum wells embedded in planar semiconductor microcavities. As an application of the formalism, we analyze the effects of the propagation through a semiconductor microcavity on a continuous-mode squeezed coherent state. In particular, we calculate the variance of the field transmitted through the microcavity in the case of strong coupling regime for different detection schemes, as a function of the detuning, the exciton–photon coupling and the exciton homogeneous broadening.

Radiative transfer in semiconductor microcavities

Two sets of quantum wells of slightly different thicknesses are grown at the antinode positions of a planar semiconductor microcavity. The excitation transfer from one set to the other, distant by 1400 Å, is studied by means of photoluminescence and photoluminescence excitation spectroscopies. The role of delocalized microcavity polariton states is emphasized.

Weak localization and nonlinear optical responses of exciton polaritons

We discuss novel nonlinear optical responses due to weak localization of exciton-polaritons (EP’s): first phase-conjugated signal induced and enhanced by the weak localization of EP’s under a single pump and a test beam which are two-photon-resonant to a biexciton. This observation will give us clear evidence of the weak localization. Second, we analyze, in terms of weak localization of EP’s, the coherent light emission in the direction normal to the surface under a single beam pumping tilted from the normal to a planar semiconductor microcavity.

Spontaneous emission control in semiconductor microcavities with metallic or Bragg mirrors

We present a systematic study of the modification of the spontaneous emission of a point dipole in a planar semiconductor microcavity, bounded by different types of mirrors. Numerical evaluations of the spontaneous emission rate indicate that semiconductor cavities bounded by Bragg mirrors display only a weak modification of spontaneous emission, while significant enhancement and inhibition of spontaneous emission should be observed in cavities bounded by metallic mirrors.

Microcavity Polaritons: Homogeneous and Inhomogeneous Broadening in the Strong Coupling Regime

The exciton-polariton states of quantum wells embedded in planar semiconductor microcavities are usually described by assuming in-plane wave vector conservation. In this work we consider the two main k(parallel to)-scattering mechanisms, namely the polariton-phonon scattering and the in-plane structural disorder of the quantum well. We calculate the homogeneous and inhomogeneous broadening of the polariton levels and show that a detailed model of the scattering processes is essential for a theoretical derivation of recently observed features of the linear spectra.

Semiconductor microcavities for spontaneous emission control

The confinement of the electromagnetic field in cavities with dimensions of the order of the wavelength modifies the characteristics of spontaneous emission of a dipole placed in the cavity. Planar semiconductor microcavities, which confine the field in only one dimension, can be readily fabricated by epitaxial crystal growth techniques. These structures display novel radiative phenomena that are of interest in basic physics and point to the possibility of developing novel optoelectronic devices.

Cavity-Polariton Mediated Resonant Raman Scattering

We present resonant Raman scattering results in planar semiconductor microcavities in the cavity-polariton regime. We demonstrate resonant enhancement of both exciton and cavity-photon nature. Evidence of cavity-polariton mediation of the scattering process is obtained from the angular dependence of the resonant Raman intensity. A single peak at the exciton energy is observed in incoming resonance scans, showing that scattering also occurs through weakly coupled localized excitons as intermediate steps.

Weak localization of exciton polaritons in a quantum well.

We describe effects of weak localization of exciton polaritons (EP's) and induced scattering of EP's into the zero-wave-vector mode in a planar semiconductor microcavity containing quantum wells (QW's). Coherent light emission in the direction normal to the surface under the tilted pumping can be explained in terms of the weak localization of EP's in QW's.

Coherent control of quantum-well excitons in a resonant semiconductor microcavity for high-speed all-optical switching

Coherent control of excitons in quantum wells embedded in a resonant planar semiconductor microcavity versus in quantum wells without the cavity at high repetition rates is investigated theoretically to determine the practical constraints for application in high bit-rate optical switching. It is shown that /spl pi/-shifted pulse pairs are optimal to coherently populate and depopulate the QW on the 100-fs timescale. For the cavity-free case, the small optical nonlinearity will require devices incorporating /spl sim/100 quantum wells; the resonant enhancement of the confined mode for the case of the cavity leads to an effective increase in the optical nonlinearity and thus a reduction of the required number of quantum wells to /spl sim/10. In addition, switch architectures that avoid interferometers, and thus will have superior temperature and mechanical stability, based on the microcavity are proposed. We believe that although room-temperature operation of a 100-Gb/s switch based on this principle may be difficult, operation at liquid-nitrogen temperature should be feasible.

Coherent control of terahertz generation in a DC-biased semiconductor microcavity

It is shown that shaped optical pulses may be used to control coherently a novel type of terahertz pulse generation from a planar semiconductor microcavity biased by a DC electric field. The new terahertz signal is due to optical rectification arising from the time-dependent polarization associated with mode oscillations. To make short terahertz pulse trains and simultaneously coherently depopulate the quantum well of excitons, specially tailored square optical pulses with nonzero area are optimal. The coherent depopulation is a strong-coupling effect and is due to the /spl pi/ phase shift in the self-consistent field (i.e., including the local-field effect associated with the exciton resonance) in the cavity that occurs in the course of a mode oscillation.

Spontaneous emission in planar semiconductor microcavities displaying vacuum Rabi splitting.

We calculate the spontaneous-emission characteristics of a quantum-well exciton embedded in the center of a planar microcavity and compare them with the emission characteristics in a single-mode cavity with lateral confinement of the electromagnetic field. The results indicate that because the modal structure of a planar microcavity consists of a spectrally dense continuum, the exciton decays into the cavity continuum with a time constant close to the free-space spontaneous-emission lifetime, even under conditions in which its spectrum displays the vacuum Rabi splitting. This behavior contrasts with the case of cavities with lateral in-plane confinement of the field, in which the vacuum Rabi splitting is the signature of a dramatic modification of the spontaneous-emission lifetime. The technological implications of this difference are discussed.